The invention concerns a transmission assembly with an infinitely variable transmission module and a constant transmission module. The transmission ratio of the infinitely variable transmission module can be continuously adjusted within certain limits in the forward and if necessary also in the reverse direction, while the transmission ratio of the constant transmission module is fixed, or adjustable in discrete steps.
In the vehicle industry, besides drive systems with conventional gear changes, infinitely variable drive concepts are also used. In this, power-branched transmissions are also used, which provide acceptable efficiency that is often lacking in an infinitely variable transmission. In power-branched transmissions part of the combustion engine""s power is transmitted via an infinitely variable transmission branch and another part of the power is transmitted via a constant, mechanical transmission branch. Having passed through their respective transmission branches, the two power flows are combined and superimposed again and then transmitted to the wheels of the vehicle via mechanical drive elements.
It is known to design the infinitely variable transmission branch as a hydrostatic, toroidal, chain, belt or electrical transmission, while the constant transmission branch can be made as a planetary gear system with integrated gear-change steps. In this context numerous combinations and variants are known to those familiar with the field.
In tractor construction, hydrostatic/mechanical power-branched transmissions are used as infinitely variable drive systems. A power-branched transmission is for example known from EP-A-0 465 752. However, the power-branched transmissions used in tractor construction have a number of disadvantages: particularly because of the large number of components and numerous variants involved, their manufacturing costs are essentially higher than the cost of ordinary part-load or full-load transmissions. The market promotes many transmission variants intended to cover different power requirements and applications. For this, in each case complete new transmissions are needed, since variants cannot be formed with known standard transmission components. The usable speed ranges are distributed in groups which can only be switched to while stationary or in ranges between which one can shift seamlessly. The seamless shift positions in question are often in the main working range of the tractor, in which the shift is perceived as unpleasant.
The objective of the present invention is to provide a transmission assembly with an infinitely variable transmission component and a constant transmission component, by means of which the aforesaid problems are overcome. In particular it must be possible to provide a large number of different transmission variants. The transmission system must satisfy various power requirements and application needs, must achieve optimum efficiency in the main working range, it must be inexpensive to manufacture, requiring a small number of different components, it must be easy to assemble, and shifting must be effected almost imperceptibly.
The transmission assembly according to the invention comprises an infinitely variable transmission component and a constant transmission component. The transmission components are formed as pre-assembled modular units that can be combined to form overall transmission systems as desired. The infinitely variable transmission module is a self-contained functional transmission unit with an adjustment gear housing, which is open on at least one side where it comprises a flange. The flange serves for the attachment, as desired, of constant transmission modules in various power categories and/or with various numbers of gear steps. Within the flange area there extends at least one infinitely variable output shaft of the variable transmission module.
The infinitely variable transmission module can produce infinitely adjustable speeds of its output shaft, and this preferably in both rotation directions. For the constant transmission modules, transmission components designed in various ways with different numbers of gear steps can be considered, in each case comprising a mechanical shift system between several gears and/or groups and if necessary including a reversing unit.
According to the invention, identical infinitely variable transmission modules can be combined with a variety of different constant transmission modules to form a series of transmissions of various power categories. In this, the constant transmission modules are designed for different powers and/or have different numbers of gear steps. The higher the nominal input power of the transmission assembly, the larger is the number of gear steps chosen for the constant transmission module.
It is particularly advantageous to design infinitely variable transmission modules for particular powers, so that they will satisfy the maximum power requirements expected from the transmission series. In this way, the number of gear steps of the constant transmission and the power loss of the transmission system overall can be kept low. Although it is more expensive to manufacture larger infinitely variable transmission modules than smaller ones, this is more than compensated by the variety of uses made possible and the associated considerable increase in the number of units manufactured. The size of the infinitely variable transmission can be restricted by the accommodation space available.
The infinitely variable transmission module is designed for a given power transfer (e.g. 200 kW for an agricultural tractor). By designing the constant transmission module with 1, 2, 3 or more transmission ratios (gears and/or groups), the infinitely variable transmission module can be adapted to the various power categories required for a tractor series. In this way, the same infinitely variable transmission module can be used in all the power categories. This is possible because, with an increasing number of gears and/or groups of the constant transmission module, the power in the infinitely variable transmission module remains the same. This means that for vehicles of lower power, the constant transmission module is made with one or only a few gears and/or groups. On transition to a vehicle the next higher power category, in each case a gear or a group is added to the constant transmission module.
The transmission series according to the invention comprises only a single infinitely variable transmission module, which can be used unchanged for a large range of vehicle categories. This enables a markedly modular structure and provides a wide variety of options for the customer, with a correspondingly more favourable cost structure. Thanks to the individuation of transmission components and the modular structure, the number of different components and the production costs are reduced to the point that they correspond to, or are even less expensive than the cost of conventional part-load transmissions in small and medium vehicle power categories and those of full-load transmissions in larger vehicle power categories. The transmission assembly or transmission series according to the invention makes it possible to assemble and dismantle the modules very simply, provides optimum efficiency in the main working range of the vehicle and has high overall efficiency throughout the speed range.
Preferably, on the side of the infinitely variable transmission module opposite the flange, a transmission input shaft is provided that can be connected to an engine and extends into the adjustment gear housing, also known as the variable transmission housing, and through the infinitely variable transmission module. The constant transmission module is fixed to the flange so that it is spatially adjacent to the infinitely variable transmission module. The infinitely variable and constant transmission branches are aligned with one another and come after one another in the axial direction. The transmission input shaft is at the same time used as an output shaft which transmits the mechanical drive power of the combustion engine directly to the constant transmission module.
It is also advantageous for the transmission input shaft to serve as the input shaft for the infinitely variable transmission module as well as the input shaft for the constant transmission module. It can also be associated with an auxiliary drive, for example in drive connection with a power take-off (PTO) shaft of the working vehicle.
A simpler transmission structure is provided by a preferred further development of the invention, according to which a shaft section extends from the input side to the output side of each transmission module. When the transmission modules are assembled together, the shaft sections are aligned with one another and are in driving connection with one another. They serve as the input shaft for the respective transmission module and/or as the drive shaft for an auxiliary drive system.
It is an advantage if, within the flange area of the infinitely variable transmission module, in addition to the infinitely variable output shaft, there also extends at least one constant output shaft in drive connection with an input shaft of the constant transmission module and aligned or parallel to the latter. The constant output shaft serves to drive a constant transmission module arranged after the variable transmission module. The term xe2x80x9cconstant shaftxe2x80x9d is used to designate shafts whose rotation speed is in a constant transmission ratio relative to the speed of an input shaft, while the speed of an infinitely variable shaft can be adjusted within certain limits in any desired transmission ratio to the speed of the input shaft.
Preferably, at least one infinitely variable output shaft of the variable transmission module extends parallel to and displaced from the transmission input shaft or as a hollow shaft concentrically with respect to a mechanically driven constant output shaft of the variable transmission module.
The infinitely variable transmission module can essentially be any type of infinitely variable transmission. For example, it can be designed as a toroidal or an electrical module. According to a preferred embodiment of the invention, however, the infinitely variable transmission module is a hydrostatic module comprising two hydrostatic units with shafts directed parallel to one another. One of the hyrostatic units is variable displacement pump, while the other hydrostatic unit is a fixed displacement motor or variable displacement motor. The hydrostatic units are attached to a mounting plate via bearings for their shafts. Preferably, at least one hydrostatically driven output shaft of the hydrostatic module is formed as a hollow shaft, through which extends concentrically a constant output shaft of the hydrostatic module. A preferred hydrostatic unit is described in a U.S. application Ser. No. 09/934,274, filed Aug. 21, 2001 commonly assigned, the specification of which is hereby incorporated by reference.
To make the hydrostatic unit as a functional and testable transmission unit in its own right, it is appropriate to fit a valve housing on the housing of the hydrostatic module, which serves the purpose of providing oil to the hydrostatic unit. For reasons of space, the valve housing is preferably attached to the hydrostatic module housing on its side facing away from the flange.
The valve housing accommodates for example an oil pump and various valves for various adjustable system pressures. It can also provide an oil flow for the lubrication and cooling of transmission components. The valve housing can accommodate an oil filter and various sensors for the measurement of pressure, temperature and flow quantity.
In a preferred embodiment of the invention, the constant transmission module comprises a summation gear which combines the output power of an infinitely variable, in particular, hydrostatically driven output shaft of the variable transmission module with the output power of a constant output shaft of the variable transmission module. In this respect, the transmission assembly can be formed in the manner of an infinitely variable hydro-mechanical power-branched transmission for work vehicles, in which the input shaft power is divided between an infinitely variable transmission module and a constant transmission module, and in which the output shaft powers of the two transmission modules are combined in a summation transmission system. The summation gear housing comprises an input flange adapted to the flange of the adjustment gear housing.
It is considered particularly advantageous to fit a planetary transmission module with an input flange adapted to the flange of the adjustment gear housing after the infinitely variable transmission module. The planetary transmission module can be formed as a so-termed planetary roll consisting of several planetary gears spatially arranged one after another, at least one of which is a summation gear system.
It is appropriate to form one or more of the successively arranged planetary gears as change-over gears, which form the constant transmission module and have one, two, three or four switching transmission ratios and/or a reversing unit. For changing between the transmission ratios, couplings and brakes are provided in the usual way. Preferably, the planetary gear module is designed so that its output shaft can provide torque in both rotation directions. A drive coupling can also be integrated in the planetary transmission.
The constant transmission module can consist of a single component but also several transmission units arranged one after the other. For example, it can consist of a summation gear module and a range module. The modules are separate transmission units, each functional in itself, that can be connected together by flanges and are arranged after one another in the axial direction.
Appropriately, the constant transmission module comprises an input flange and an output flange, respectively located on opposite sides of the transmission housing. If desired, further constant transmission modules of different power categories and/or with different output levels can be attached to the output flange.
Preferably, a further constant transmission module of this type is formed as a range module with at least one group. The range module can be connected by means of an input flange to an output flange of a previous constant transmission module, in particular, a summation gear housing or a planetary gear module. Its drive shaft is coupled in driven connection to an output shaft of the previous constant transmission module. The transmission assembly appropriately comprises three transmission modules: an infinitely variable transmission module, formed as a hydrostatic unit, a first constant transmission module formed in the manner of a planetary gear module with a summation portion and if desired with a gear range portion, and a second constant transmission module formed as a group transmission module.
If economically viable from the production standpoint, the housing of the first constant transmission module and the second constant transmission module formed as a range module can be made as a common housing component. This provides a housing component open at both ends and having in the middle a partition wall that serves to support the drive shafts. Besides, the housing component has two flanges, such that the input flange is connected to an output flange of the infinitely variable transmission module and the other flange can be connected as output flange to a differential housing or to a rear axle housing of a vehicle.
It is also advantageous to provide a partition wall between two transmission components which prevents the passage of lubricant between them. This makes it possible to use transmission units together which have different requirements in relation to lubricant quality. The partition wall can for example separate a first transmission space containing the hydrostatic unit with its strict lubricant quality requirements, from a second transmission space accommodating mechanical transmission components with less severe demands in terms of lubricant quality.